Report Summary

Analysis of organic compounds and organisms in deteriorating stonework

A study has been carried out to characterize organic compounds and organisms present in weathered stones. Analysis was carried out by solvent extraction or by analytical pyrolysis, a flash thermal desorption and degradation method, which only requires microgram quantities of samples.

The black sulphated crusts deposited on the surfaces of historic buildings and monuments are composed of inorganic materials (mainly gypsum) and a complex mixture of organic compounds entrapped in the mineral matrix. There is a strong similarity between compounds present in the gaseous and particulate phases in urban atmospheres and those encountered in black crusts, (eg petroleum derivatives, smoke particles from wood combustion, biogenic components of aerosols).

Endolithic and epilithic cyanobacteria and algae were isolated from European cathedrals. Combining observations in both field and laboratory materials enabled analysis of the processes of colonization and development of cyanobacterial algal communities in the stone, as well as the mechanical deterioration produced. Some basic studies on diazotrophic growth of cyanobacteria were also undertaken. Fungi were found to be associated with cyanobacterial algal biofilms in building stones, from which they most probably derive much of their carbon requirements. They produced organic acids, which decompose mineral matter. Lichens and bryophytes were shown to be deterioration agents in different building materials. The colonization by these organisms gives rise to the later invasion by vascular plants, whose roots cause important deterioration in the structure of buildings. Lack of cleaning and maintenance of historic buildings and monuments is considered to be one of the major factors contributing to biological colonization and deterioration.